The present invention relates generally to voltage regulators, and more particularly to control systems for switching voltage regulators.
Voltage regulators, such as DC to DC converters, are used to provide stable voltage sources for electronic systems. Efficient DC to DC converters are particularly needed for battery management in low power devices, such as laptop notebooks and cellular phones. Switching voltage regulators (or more simply xe2x80x9cswitching regulatorsxe2x80x9d) are known to be an efficient type of DC to DC converter. A switching regulator generates an output voltage by converting an input DC voltage into a high frequency voltage, and filtering the high frequency voltage to generate the output DC voltage. Typically, the switching regulator includes a switch for alternately coupling and de-coupling an unregulated input DC voltage source, such as a battery, to a load, such as an integrated circuit. An output filter, typically including an inductor and a capacitor, is coupled between the input voltage source and the load to filter the output of the switch and thus provide the output DC voltage. A controller measures an electrical characteristic of the circuit, e.g., the voltage or current passing through the load, and sets the duty cycle of the switch in order to maintain the output DC voltage at a substantially uniform level.
Voltage regulators for microprocessors are subject to ever more stringent performance requirements. One trend is to operate at higher currents, e.g., 35-50 amps. Another trend is to turn on or off different parts of the microprocessor in each cycle in order to conserve power. This requires that the voltage regulator react very quickly to changes in the load, e.g., several nanoseconds to shift from the minimum to the maximum load. Still another trend is to place the voltage regulator close to the microprocessor in order to reduce parasitic capacitance, resistance and/or inductance in the connecting lines and thereby avoid current losses. However, in order to place the voltage regulator close to the microprocessor, the voltage regulator needs to be small and have a convenient form factor.
In addition to these specific trends, high efficiency is generally desirable in order to avoid thermal overload at high loads and to increase battery life in portable systems. Another desirable feature is for the voltage regulator to have a xe2x80x9cstandby modexe2x80x9d which consumes little power at low loads.
Conventional controllers are constructed from analog circuits, such as resistors, capacitors and op-amps. Unfortunately, analog circuits are expensive and/or difficult to fabricate as integrated circuits. Specifically, special techniques are needed to fabricate resistors and semiconductor devices. In addition, analog signals can be degraded by noise, resulting in a loss of information.
In view of the foregoing, there is room for improvement in voltage regulators and control systems for voltage regulators.
In general, in one aspect, the invention is directed to a method of operating a voltage regulator which has an input terminal coupled to an input voltage source, an output terminal coupled to a load, and a plurality of switching circuits to alternately couple and decouple the input terminal to the output terminal. The method calculates an estimated current for each switching circuit, each estimated current representing a current passing through an inductor associated with the switching circuit. A total desired output current to pass through the inductors is calculated which will maintain an output voltage at the output terminal substantially constant. The switching circuits are controlled based on the estimated current and the total desired output current so that a total current passing through the inductors is approximately equal to the total desired output current.
In another aspect, the invention is directed to a voltage regulator having an input terminal coupled to an input voltage source and an output terminal coupled to a load. A plurality of switching circuits intermittently couple the input terminal and the output terminal in response to digital control signals. A plurality of filters, each including an inductor, provide a generally DC output voltage at the output terminal. A plurality of current sensors generate feedback signals derived from the currents passing through the switching circuits. The digital controller receives and uses the plurality of feedback signals to calculate an estimated current for each switching circuit. Each estimated current represents a current passing through the inductor associated with the switching circuit. A total desired output current to pass through the inductors is calculated which will maintain an output voltage at the output terminal substantially constant. The digital control signals are generated based on the estimated currents and the total desired output current so that a total current passing through the inductors is approximately equal to the total desired output current.
In another aspect, the invention is directed to a method of determining a total desired current through a switching circuit in a voltage regulator in order to maintain an output voltage at an output terminal substantially constant. The switching circuit intermittently couples an input terminal to be coupled to an input voltage source to the output terminal to be coupled to a load. The voltage regulator includes at least one capacitor coupled to the output terminal. A first output voltage is measured at the output terminal at a first time, and a second output voltage is measured at the output terminal at a second time. An estimated current representing the current flowing through the inductor is calculated, a capacitance current representing a current flowing to or from the at least one capacitor is calculated based on a difference between the first output voltage and the second output voltage, and a correction current is calculated based on a difference between a desired voltage and one of the first and second output voltages. The total desired current for the voltage regulator is calculated from the difference between the sum of the estimated current and the correction current, and the capacitance current.
Advantages of the invention may include the following. The voltage regulator handles relatively large currents reacts quickly to changes in the load. The voltage regulator may use small capacitors with a convenient form factor. The voltage regulator can include multiple slaves which are operated out of phase in order to reduce current ripple. The use of analog circuits is minimized by converting analog measurements in the controller into digital signals. The controller may be implemented using mostly digital circuitry, and may be fabricated using known processes through conventional complementary metal oxide semiconductor (CMOS) fabrication techniques. This reduces the number of off-chip components in the controller. The controller operates with a digital control algorithm in which the operating parameters may be modified to adapt the voltage regulator for different applications. The digital control algorithm can operate at clock frequency significantly higher than the switching frequency, allowing quick response to changes in the load. The master and slaves can communicate with digital signals, thereby providing improved communication reliability.